Fundamental Physics with VHE Cosmic Gamma Rays Manel Martinez DISCRETE’08, Valencia 16/Dec./2008

Outline: 0- Introduction 1- Cherenkov Telescopes 2- Dark Matter 3- Speed of light invariance 4- Outlook

0- Introduction

VHE Cosmic Gamma rays: highest energy electromagnetic radiation from our Universe Presently: Highest energy messengers detectable from our universe which: - Are stable particles => cosmological distances - Interact enough to be “easily” detected => modest and simple detectors - Are not deflected by cosmic magnetic fields => allow to pinpoint and identify the source with high precision

=> Highest energy wide-open window for the observation of our universe VHE GAMMA-RAY ASTRONOMY VHE Cosmic Gamma rays: highest energy electromagnetic radiation from our Universe

Origen Propagation Studies Source Studies

VHE gamma rays are produced in the most energetic and violent phenomena in the universe: A ) COSMIC ACCELERATORS - Hadron accelerators: p X ->  -> gamma 1) Study the source: production mechanisms -- 00 ++  (TeV) p + (>>TeV) matter hadronic acceleration

log(E) log(energy density) eV keV MeV GeV TeV SyIC - Electron accelerators: synchrotron: e B -> e gamma + inverse Compton: e gamma -> gamma e e - (TeV) Synchrotron  (eV-keV)  (TeV) Inverse Compton  (eV) B leptonic acceleration

B ) HEAVY PARTICLE ANNIHILATION OR DECAY Through the annihilation or decay of very massive or energetic objects: dark matter, very massive particles at unification scales, relics of universe phase transitions, primordial black holes,… => Tool to search for new, massive, particles and objects.

VHE gamma rays are, so far, the most energetic messengers reaching us through a determinable path: explore the structure of intergalactic medium: - at long distances: produced in sources at cosmological distances from us - at the shortest distances: they explore space-time at the highest energies => they may allow us to address important questions in fundamental physics and cosmology 2) Study the propagation in the cosmic medium

1- Cherenkov Telescopes

Gamma- ray ~ 10 km Particle shower Detection of TeV gamma rays using Cherenkov telescopes ~ 1 o Cherenkov light ~ 120 m Observation Technique

Image intensity  Shower energy Image orientation  Shower direction Image shape  Primary particle

Better bkgd reduction Better angular resolution Better energy resolution Systems of Cherenkov telescopes Slide fro Pr W. Hofmann

OG 1 VHE Experimental World STACEE CACTUS MILAGRO TIBET ARRAY ARGO-YBJ PACT GRAPES TACTIC MAGIC HESS CANGAROO TIBET MILAGRO STACEE TACTIC

Very special moment in VHE Cosmic gamma-ray observation: real revolution in consolidation of Cherenkov telescopes as astronomical instruments => transition from “HE experiments” to “telescopic installations” --> exploding interest in the astronomical community… ! Big observational step in the last few years: - quantitative ( x10 number of detected sources) - qualitative (extremely high quality => unprecedented detailed studies). => DOWN OF A GOLDEN AGE FOR CHERENKOV TELESCOPES !

W. Hofmann - Texas Symposium 2006 Over 70 sources detected already (and increasing steadily...) :

OG 1 SNRs Cold Dark Matter Pulsars GRBs Speed of light invariance Cosmological  -Ray Horizon AGNs The VHE  -ray Physics Program The VHE  -ray Physics Program Origin of Cosmic Rays Binary systems Galactic Extragalactic

2- Dark Matter

Dark Matter annihilates producing gammas as secondary particles. Expected gamma flux proportional to (  DM ) 2 x D -2 x  => Most promising targets: - Galactic Center, - Dwarf Spheroidal Satellites (large M/L ratio), - Subhalos, - Microhalos, - Intermediate Mass Black Holes (IMBH), - Local Group Galaxies, - Globular Clusters.

Galactic Center SGR A Point-like core Extended tail Similar to NFW profile -> Consistent with SGR A* to 6’’ and slightly extended. -> No significant variability from year to minute scales (in ~40 h obs. time distributed over 2 years) syst. error

Dark matter annihilation ? 20 TeV Neutralino 20 TeV KK particle proposed before H.E.S.S. data proposed based on early H.E.S.S. data  J. Ripken ICRC 2005 Preliminary

Gamma ray spectrum Preliminary Unbroken power law, index 2.3 Preliminary Good agreement between HESS and MAGIC (large zenith angle observation).  Very unlikely to be dark matter.  Presence of a strong gamma-ray source outshines any possible DM signal

The Galactic Centre Ridge Same map after subtraction of two dominant point sources => Clear correlation with giant molecular clouds traced by their CS emission Galactic Centre gamma- ray count map HESS

So far, efforts to detect DM annihilation with VHE gammas have been unsuccessful but It turns out that VHE gamma-ray astronomy provides probably the best tool to try to unveil the nature of DM: - LHC -> may find candidates (SUSY, extra-dimensions,...) but cannot prove that they are the observed Dark Matter - Direct searches (nuclear recoil) -> may recognize local halo WIMPs but cannot prove the nature and composition of Dark Matter on the sky. - Indirect searches: * Charged particles -> may detect excesses but not map them into the gravitationally identified density profiles. * Neutrino telescopes -> may need many KM3 to reach the sensitivity attainable to VHE gamma ray installations. * Gamma satellites -> may have too limited lever arm to pinpoint DM spectral features.

Note 1: Direct Searches and Indirect Searches look at different things: - Direct searches: WIMP-hadron interaction -> interaction of Dark Matter with ordinary matter -> lose constraints -> impact on barionic compression. - Indirect searches: WIMP-WIMP annihilation -> same process causing relic abundance -> cosmological constraints -> impact on fundamental cosmology Note 2: LHC (and ILC) reach limited to neutralino masses of <~300 GeV. Beyond that only ground based instruments will be able to provide additional constraints on SUSY parameter

-> the role of VHE gamma-ray astronomy for Dark Matter studies, even beyond the discovery, is UNIQUE: ”Gamma-ray observations provide the only avenue for measuring the dark matter halo profiles and illuminating the role of dark matter in structure formation”. AGIS white book

In addition, in the coming next few years: - LHC will have crutial information on particle candidates - Fermi (GLAST) may have found a plethora of “dark sources” already - Astronomical surveys (SDSS, PanSTARRs, DES,...) will have identified a pretty large number of (nearby) objects with large mass/light ratio. - Improved calculations/simulations will allow more precise predictions.

Contribution of Internal Bremstrahlung T.Bringmann, L.Bergstrom, J.Edsjo 2007

Sommerfeld Enhancement for slow WIMPS (non-tidaly disrupted clumps) M.Lattanzi and J.Silk 2008

=> there are very good prospects for VHE gamma ray astronomy playing a key role for the understanding of the nature, properties and distribution of Dark Matter in the next coming years. Or even: - The results of DAMA, PAMELA, ATIC, etc... might have been confirmed as DM signals.

3- Speed of light invariance

Space-time at large distances is “smooth” but, if Gravity is a quantum theory, at very short distances it might show a very complex ( “foamy” ) structure due to Quantum fluctuations. A consequence of these fluctuations is the fact that the speed of light in vacuum may become energy dependent. The energy scale at which gravity is expected to behave as a quantum theory is the Planck Mass E QG = O(M P )= O(10 19 ) GeV E QG = O(M P )= O(10 19 ) GeV

From a purely phenomenological point of view, the effect can be studied with a perturbative expansion. The arrival delay of  -rays emitted simultaneously from a distant source should be proportional to the path L to the source and a the difference of the power n of their energies: The expected delay is very small and to make it measurable one needs to observe very high energy  -rays coming from sources at cosmological distances which emit gammas with a sharp time structure

Gamma rays of high energies (E) Cosmological distances (D) Short duration transients in time profiles Pulsars, E up to 2GeV, D about 10 kpc, (Kaaret, 1999) AGNs, E up to 10 TeV, D about 100s Mpc (Biller, et al, 1999) 35 GRBs, E up to MeV, D beyond 7000 Mpc (Ellis, et al, 2005) < ms < minutes < 100 ms Results before MAGIC and HESS: A.Sakharov 2007

MAGIC observation of Mkn 501 flare  in 2005 (z=0.034)

Astrophys.J. 669, 862 (2007)

MAGIC Results (ECF Method): Linear Quadratic 95% CL Phys.Lett B668, 253 (2008)

Caveat: how to disentangle propagation delays from source-intrinsic delays ?. a) observe sources at different redshifts and check delay proportional to distance. b) use geometrical time stamps (pulsars).

a) sources at different redshifts…

Crab Flux Benbow 1221 Paneque 1098 HESS 28 th July 2006 HESS observation of PKS 2155 flare  in 2006 (z=0.116)

- No visible delay - M QG1 > 0.6 x GeV - Does not contradict MAGIC GeV >800 GeV

b) geometrical time stamps…

EGRET Pulsars

MAGIC detection of the Crab Pulsar Science 322 (2008) 1221 Detailed analysis ongoing.

What next ?. GRBs: (try to catch them at VHE) - Good timing, very large distance, low energies (-> linear term) - Better statistics are expected with GLAST. - A MAGIC detection around 100 GeV would probably yield to very good sensitivity to energy-dependent time delays. AGNs: (wait actively for next flare) - Bad timing, large distances, high energies (-> quadratic term) - Distance can improve with better sensitivity instruments, but paying the price of lower energies due to EBL. Timing can improve also with sensitivity. Pulsars: (try to observe them at VHE) - Very good timing, very short distance, low energies (-> linear term) - With better instruments the time resolution will improve and the detected energy might still increase a bit. - If GLAST and MAGIC pulse shapes are similar, a combined analysis may give competitive limits.

4- Outlook

Fermi (GLAST) Major HE gamma-ray instrument. Thousands of new HE sources expected. LAT: coverage from 20 – 300 GeV. Launched in May Many discoveries and new results coming... Satellites

MAGIC-II New, improved 17m telescope. Faster FADCs (up to 4Gsps) and a better high-QE camera. Factor 2-3 improvement in sensitivity. First light in Cherenkov Telescopes - 1

HESS-II New 28m telescope pixel camera. Lower energy threshold GeV First light in 2010 Cherenkov Telescopes - 2

What next ? The present generation of ground instruments may detect and study around 100 sources, but a lot of physics potential still open…

C TA An advanced facility for ground-based high-energy gamma ray astronomy Possible CTA sensitivity Crab 10% Crab 1% Crab GLAST MAGIC H.E.S.S. E. F(>E) [TeV/cm 2 s] few very large telescopes densely packed many small telescopes spread in a very large area many medium size telescopes covering a large area

C TA An advanced facility for ground-based high-energy gamma ray astronomy Not to scale ! Aims to explore the sky in the 10 GeV to 100 TeV energy range with ~10 better sensitivity and better energy and angular resolution. Builds on demonstrated technologies. Combines guaranteed science with significant discovery potential. Full sky coverage: South array ~100M€ North array ~50M€

C TA An advanced facility for ground-based high-energy gamma ray astronomy Status and Outlook - ASPERA-ApPEC give full support to CTA in its roadmap. - CTA also included in the ASTRONET roadmap. - Recently included in the ESFRI updated roadmap > Technical Design Report > Preparatory Phase (Array Prototyping) > Array Construction partial operation could start already in

Summary: Summary: - VHE gamma astronomy may play an UNIQUE role in the understanding of Dark Matter and other Fundamental Physics issues. - VHE gamma astronomy is today in a golden age and the prospects for tomorrow and the near future are even more exciting… stay tuned !.